Powering CCTV and Security Systems: Constant Voltage Drivers Beyond Lighting

Security cameras are powered by the same low-voltage DC technology that drives LED lighting, and the same constant voltage power supplies serve both industries. A CCTV installation — cameras, recorders, and accessories — is a distributed DC load connected over distance, and the engineering questions are familiar: voltage drop in the cable, current draw at the camera, centralized versus distributed power, and protection against shorts and overloads. For a manufacturer that produces both LED drivers and CCTV power supplies, the common design principles are worth explaining to customers in both markets, because the same mistakes occur in both.

The first question in a CCTV design is the camera's actual current draw. A camera's datasheet may state a maximum current — an IP camera with IR LEDs, heater, and motorized lens can draw 800mA to 2A at 12V or 24V AC/DC — but the average draw is often far lower. The power supply must be sized for the worst case, not the average: a 16-camera system with cameras averaging 500mA but peaking at 1A needs a supply that can deliver 16A, not 8A. The standard practice is to sum the peak currents of all cameras and size the supply at 80 percent of its rating — the same derating rule used for LED drivers. An 8-output CCTV power supply rated at 60W, delivering 12V and roughly 5A total, can feed a modest camera bank, but the installer must verify the per-channel rating and the total.

Voltage drop is the second issue, and the calculation is identical to LED lighting. Cameras are sensitive to supply voltage: a 12V camera that receives 11V may fail to start its IR LEDs, may produce image problems, or may behave erratically. The standard design target is to keep the voltage at the camera within 10 percent of nominal, and preferably within 5 percent. For a 12V system, a 5 percent drop is 0.6V; using the two-wire drop formula (2 × I × L × R), a 30-meter run at 1A with 1.0mm² cable (0.017 ohm/m) drops 2 × 1 × 30 × 0.017 = 1.02V — 8.5 percent, above the 5 percent target. The solution is larger cable (1.5mm² gives 0.69V, 5.7 percent) or a 24V distribution with a local step-down at each camera. Many modern systems solve this by using PoE (Power over Ethernet), which centralizes power at the switch and lets the cable length and IEEE 802.3af/at power budgets handle the distribution.

Centralized versus distributed power is a genuine design decision. A centralized supply — one multi-output unit in a cabinet — is simpler to maintain, has a single point of protection, and is easier to back up with a UPS. A distributed supply — small adapters at each camera — eliminates the long DC runs and their voltage drops, but multiplies the number of failure points and makes maintenance less convenient. The 60W, 8-output CCTV supplies are the classic centralized solution: each output has its own fuse or polyfuse, the total power is shared across the bank, and the unit mounts in a security cabinet with the DVR. The per-channel protection is critical — without it, a shorted camera cable takes down the entire system.

The power supply's protection features matter as much as its rating. Overload protection (the supply folds back or shuts down rather than burning), short circuit protection per channel, and over-temperature protection are standard requirements. The supply should also tolerate the camera's startup inrush — many cameras draw a higher current during startup as their IR LEDs and motors energize. A supply with a soft-start circuit or sufficient headroom avoids the 'all cameras reboot when one starts' phenomenon that plagues undersized centralized units.